In the past several years, many new techniques have been developed to perform assays for biological substances. Most of the conventional procedures for performing immunoassays require the separation of unreacted constituents from the mixture after an immunoreaction has occurred. This separation step is usually cumbersome, inconvenient, and time consuming. In addition, procedures including a separation step are not well adapted for continuous flow or automated apparatuses. Therefore, it is desirable to accomplish an assay which does not require separation of bound and unbound reactants. Voltammetric analysis of immunoreactions is such an assay method.
One of the drawbacks of using voltammetric techniques for immunoassays, however, has been low sensitivity. In a recent publication from W. R. Heineman, H. B. Halsall, and C. W. Anderson, Immunoassay by Differential Pulse Polarography, Science, Vol. 204, Pgs. 865-866; 25 May, 1979, a voltammetric technique for performing immunoassays is described. Also, see Science, vol. 204 No. 865 (1979); and Analytical Chemistry, Vol. 51, No. 12, October, 1979. The described technique appears to be too insensitive for measuring biological samples, wherein many analytes of interest are found in very low concentrations.
Therefore, in order to provide a viable voltammetric immunoassay technique, a marked improvement in the sensitivity of the voltammetric techniques is needed. The present invention is addressed to enhancing such sensitivity.